This is an application for the acquisition of a Shared Light Microscope and Image Analysis System under the Shared Instrumentation Grant Program of the Division of Research Resources. The requested instrumentation will provide shared access to a number of primary users with USPHS, NIH-supported research projects ranging from the study of hormone-induced membrane recycling in epithelial cells, through radioautography of neurotransmitter receptors in brain slices, to the molecular biology of regulation of prolactin gene expression in brain and pituitary. Several areas of cell biology, neurobiology, molecular biology, neuropharmacology, electrophysiology and receptor mechanisms are covered by this research. An extended community of users within the Institution is also identified in the application; this interdepartmental and interdisciplinary group of biomedical scientists will achieve optimal use of the advance instrumentation requested in the application. The considerable contribution of the requested instrumentation to the scientific capabilities necessary to further the ongoing research projects is described, as is the impact of the shared, interdisciplinary effort centered on the instrumentation but pervading the thinking of the users of this facility and their research students. These have already become evident since the early stages of analysis and planning for the shared resource. The designated team of supervisors of the facility is trained in microscopy, cytochemistry and morphometry, and in scientific data analysis and computing, respectively. Additional expertise is provided by the already functioning advisory board which includes an expert in morphometric image analysis and microscopy. The documented and widely based need for this resource in the Institution justifies a strong commitment to the housing, maintenance and use of the shared instrument. The Department of Physiology and Biophysics has therefore committed space for the facility, will provide a special contribution to the salaries of the principal investigator/supervisors, and will be responsible for the financial arrangements to cover the maintenance costs. Extensive technical analysis and practical data show that the Zeiss Axiomat System meets all the identified needs of the user community described in the application. Nevertheless, careful exploration of other alternatives in combined microscopy and image analysis that would serve the needs of the entire group of users within the Institution is undertaken on a continuous basis until the funding of the requested instrumentation is completed.